1. Technical Field
The object of this invention is a process for spatially coordinating several images of the same object obtained either by a transparency projection or by photographic-type reproduction.
2. Related Art
The use of fixed equipment for taking for example X-ray images, of objects from different angles, in order to obtain the data required to reconstruct three-dimensional images, presents drawbacks in terms of space required, stability and cost. However, such equipment has been employed until now to provide accurate coordination between the images; such coordination being required in order to reconstruct the volume represented by these images. The most common examples are body scanners.
In most cases, the raw elements produced by the analysis are displayed on two-dimensional images such as, for example, radiographs. On such images, the characteristic of each point of the image is a result of the cumulative characteristics of all the points of the object being projected at that point of the image.
In order to obtain all of the required information, the observer must, in many instances, view an object from several different angles; however, the observer in this case often experiences difficulties in coordinating the various available images.
Modern technology increasingly relies on computer-aided reconstruction techniques, as in the case of the body scanner.
More generally, computer processing of several interrelated images requires that the said images and the sources generating them be precisely positioned in relation to each other and to the objects such that, during processing, it will be possible to unequivocally determine the exact position in space of all the rays forming the points of the various images.
In the text which follows, the word source is employed to designate the point in space from which diverge the various rays contributing to form the image (for example, X-ray source in radiography, objective in photography).
The same problem is encountered when, for example, it is necessary to correlate images obtained using different processes such as, for example, radiography and scintigraphy.
In order to achieve the desired result, the practice which comes to mind consists of maintaining the object to be observed in a fixed, specific position in relation with the means of observation, which are also located in a precise manner. More particularly, it is then essential that the object be immobilized while the series of views are taken. This practice is constraining and significantly restricts the possibilities of taking views.
The object of this invention is to propose a process to provide unequivocal definition for each image of the position of the source and of the plate supporting said image relative to the object, thus providing a precise coordination of images between themselves, without requiring the use of heavy and costly fixed equipment.
According to a particular application of the invention, the process for spatially coordinating several images of the same object obtained by projection onto one or more image planes using at least two sources is characterized by the following steps:
a) associating to the object at least one set of at least five points connected in a fixed position relative to the object and called markers, wherein at least four of said points are located in a plane called the reference plane and at least one of said points lies outside said reference plane, wherein the nature and position of said markers are such that they appear on said images and may be identified individually;
b) determining, from the respective projections of said markers lying in said reference plane on each of said image planes related to said sources, the respective directions of the intersections of each of said image planes with said reference plane;
c) then determining, from the respective projections ions of said outside markers, the position of each of said sources relative to said reference plane and that of each of said image planes;
d) coordinating, by identifying the positions of said image planes and of each of said sources relative to said set of markers, the various lines which produce the projections of said object on each of said image planes.
The use of such a system gives the possibility of taking a series of pictures while leaving to the object some latitude in movement, either by using a single picture-taking system and moving the object, or by moving the picture-taking system around the object or, finally, by using two different viewing processes, wherein the only and easily satisfied requirement is that the markers connected in a fixed position relative to the object be visible on all the images.
The discovery of the properties of a set of markers according to the invention that permit coordination of several images of the same object discloses an unexpected feature in that the inventor has demonstrated that other systems comprising, for example, only three points defining a plane and one point lying outside that plane, or five coplanar points, do not solve the general problem of image coordination. The idea of combining at least four coplanar points with at least one outside point to obtain a set of markers offers, in this respect, an unexpected and novel solution to the problem.
According to a preferred embodiment of the invention, there are five marker points; four of these points form the vertices of a tetrahedron, while the fifth lies on one of the faces of this tetrahedron. Indeed, considering a figure of four points in one plane, projected onto another plane from a source at a finite distance, it can be demonstrated that once the initial figure and its projection on another plane are known, the direction of the intersection of the two planes can be determined. Once this direction is known, it is then possible to determine the correspondence of all the points in the image plane with what would be the reversed projections of these points on the plane of the initial figure and, in particular, the position of the projection of the outside point on the plane of the initial figure and, consequently the direction of the source at that point. Once this direction is known, the other points are used to locate both the source and the plane of the projected figure relative to the markers.
Thus, it is possible to determine the relative locations of the image plane, the source, and the markers, and consequently of all the projection lines in space forming the images of the object.
However, when the sources lie at infinity and the projection is therefore cylindrical, four points are sufficient, wherein three of these form a reference plane and the fourth lies outside this plane.
In addition, when the reference plane and the image plane are parallel to each other, the intersection of the two planes is at infinity. Two points are then needed outside the reference plane in order to establish the position of the source and that of the image plane. A limiting situation occurs in the case wherein the reference plane and the image plane are not only parallel but also substantially coincident.
According to another aspect of this particular embodiment of the invention, it is possible to spatially coordinate several images of the same object, obtained by projection on an image plane and related to at least two sources. The process is then characterized by the following steps:
A) associating to the image plane a reference plane related to said object which is subtantially coincident with said image plane and a system of markers comprising at least two pairs of markers comprising at least two points lying in said reference plane and at least two points lying outside said reference plane, wherein the lines connecting each outside point to the corresponding point in said reference plane are parallel and define a cylindrical projection direction;
B) determining the positions of said sources from the projections of said outside points on said reference plane;
C) determining from the positions of said markers lying in said reference plane, the projections of said sources parallel to said connecting lines and their positions in space, relative to said projections of said outside points;
D) then determining, from said cylindrical projections of said sources and from the respective projections of the points of said object, the cylindrical projections of said points of said object on said image plane and their spatial dimensions;
E) then determining, from said cylindrical projections of said sources on said image plane and the respective projections of the object on said image plane and from said sources, a polyhedron defined in said image plane, delimiting the cylindrical projection of said object along said direction of cylindrical projection, and
F) determining, from said spatial positions of said sources and from the projections of said object, obtained from said sources, an enclosed, three-dimensional space containing said object.
Thus, this particular embodiment of the process according to the invention takes into account a situation encountered in practice wherein the reference and image planes are coincident. In this case, the function of the markers according to the invention is to locate an object in space as well as the various sources employed in the process.
In all of the embodiments of this particular aspect of the invention, whether there are five markers (four coplanar points and one point lying outside the plane), or when the reference plane and the image plane are parallel (three points defining a plane and two points lying outside the plane) or coincident (two markers in the reference plane and two outside points), or wherein the sources are at infinity (four points), the procedures employed in carrying out the different steps of the process are similar: determining the positions of the sources relative to the set of markers, then the position of the image plane and, once the positions have been determined, locating in space the rays producing the images of the object in relation with the set of markers.
The essential difference between these two aspects of the process according to the invention lies in the fact that the number of spatial unknowns that needs to be determined is smaller in the latter aspect of the invention (coincident image plane and reference plane) than the number of unknowns considered in the first aspect, wherein determining the relative position of the image plane relative to that of the reference plane requires determination of nine unknowns.
When the two planes are coincident, two of the four coplanar markers of the process are superfluous and two markers lying in the reference plane, each associated to a marker outside this plane, are sufficient. However, as in the first aspect of the process, it is possible to provide several coplanar marker points and several outside marker points which, in practice, contribute, by their redundancy, to increasing the accuracy of the image coordination process.
According to another aspect of the invention, a device for carrying out the process comprises means to obtain projections on image planes of at least one object by the transmission of waves affected-by passage through this object from sources of these waves the device further comprising:
marking means connected in a fixed position relative to the object and defining at least one reference plane, wherein the nature and position of said marking means are such that they appear on said images and may be identified individually; PA0 means for determining the directions of the respective intersections of said image planes with said reference plane; PA0 means for determining the respective positions of said sources relative to said marking means; PA0 means for determining the respective positions of said image plane relative to said marking means; and PA0 means for coordinating said projections of said object from said positions.
Thus, using the device according to this particular embodiment of the invention, it is possible to coordinate several different projected images when, because the object has moved between taking each of the images, the relative position of the image planes and of the sources relative to the reference plane, and therefore to the object, has changed.
According to a still further aspect of the invention, the process for spatially coordinating several images of the same object subjected to irradiation causing secondary emissions, such as neutron, flux, obtained on one or more image planes from internal radiation sources induced said object, is characterized by the following steps:
A) associating to the object at least one set of at least five points connected in a fixed position relative to the object and called markers, wherein four of said points form a reference plane and wherein at least one of said points lies outside said reference plane, wherein said markers are of a nature such that, after collimation, they provide traces on said images and are positioned such that they appear on said images and may be identified individually;
B) determining, after collimation, on each image produced by said internal sources, the trace of said markers lying in said reference plane and that of said outside point;
C) then determining, after collimation, on each image produced by said internal sources, from the traces of said markers, the directions of collimation and the respective positions of each of said image planes relative to said reference plane; and
D) then positioning in space the different collimation lines producing the images of said object on each of said image planes relative to said reference plane.
The process may thus be applied to images obtained by using radiation emitted by an object either from internal sources, such as in scintigraphy, or from external sources, as in the emissions induced by a neutron flux or any other excitation flux, including light rays. The sources are then no longer external to the object but are present on or induced in the object itself.
The device for implementing the process according to the invention in the area of scintigraphy, or in that of induced emissions, comprises:
A) marking means capable of emitting the radiation and defining at least one reference plane and one outside point, wherein the nature and position of said marking means are such that their traces appear after collimation on said images and they may be identified individually;
B) means of determining the collimation directions and the respective positions of said image planes relative to said marking means, from said traces of said marking means; and
C) means of spatially coordinating the rays producing the images of said object, from the respective positions of said image planes and said collimation directions relative to said marking means.
This device may also be employed with image coordination devices implementing means which influence the transmission of waves emitted by external sources, such as those described in the foregoing, either by selecting markers of a type such that their traces appear in all of the imaging processes employed, or by using sets of markers which are specific to each case but geometrically interrelated. It is thus possible to associate, for example, radiography and scintigraphy, or neutron imaging, and the images formed by emissions induced by the neutron flux, by providing marker systems adapted to each investigational technique.
The aforesaid processes and devices provide geometric solutions to the problem posed.
The applicant has discovered that the problem of the invention could also be solved using an algebraic solution.
According to this aspect of the invention, the process for spatially coordinating several images of the same object obtained either by a transparency projection or, for instance, by photographic reproduction, wherein these images are obtained from a number n of means on a number n of image planes or surfaces which are coincident or not coincident, is characterized by the following steps:
A) using a set composed of a number p of observable and identifiable points which pre-exist on the objects or are connected in a fixed position thereto and the traces of which are visible on all of the images;
B) determining, from the set of traces of said points on the various images, in a practical system of reference, the coordinates of the various sources, the identifiable points and the image surfaces;
C) these coordinates being calculated using a set of linear equations deriving from the alignment of the points of their images and of the origin of the rays used to form said images of said points; and
D) representing this set of relations by a matrix which can be solved if the relation 2pn 9n+3p-S is satisfied, where S represents the number of known geometric relations existing in the system, whereby this relation determines the minimum number of points required.
Other features and advantages of the invention shall b apparent in the description which follows.